Starting arrangement for electric discharge devices



Oct. 19, 1948. 0, D. HINMAN I I 2,451,330

STARTING ARRANGEMENT FOR ELECTRIC DISCHARGE DEVICES Filed Nov. 21, 1944H5 ATmRA/E Patented Oct. 19, 1948 STARTING ARRANGEMENT FOR ELECTRICDISCHARGE DEVICES Donald D. Hinnian, Cleveland Heights, Ohio, assignorto General Electric Company, a corporation of New York ApplicationNovember 21, 1944, Serial No. 564,479

7 Claims.

This invention relates to the starting control of electric dischargedevices, and is very useful for fluorescent tubes of positive columndischarge type, as well as for various other discharge devices. Theinvention is especially adaptable for starting discharge devicesquickly, without the delay usually entailed by prehearing theircathodes.

As is well known, the voltage required to start a discharge through anionizab-le atmosphere (gas or vapor, or both) is considerably higherthan that required to maintain it after it has started. Even thisoperating voltage is often different from ordinary lighting supplycircuit voltages, so that a transformer is generally interposed betweenthe supply circuit and the discharge circuits of an installation, togive the required voltage. In any case, current-limiting chokes orballasts are commonly interposed in the discharge circuits. Suchballasts usually. have inductance, and may also include capacitance.Very commonly, the ballast is structurally built into the transformer.In the case of D. C. discharges, means other than transformers areemployed to give the desired voltage, but resistive or reactive ballastsare still used to control the discharge current.

Most fluorescent lamps of positive column low pressure dis-charge typeare at present hot-starting, with flow of heating current through theircathodes to preheat them before discharge is initiated. For thispurpose, a starting circuit with an automatic switch therein isconnected across the discharge circuit, in parallel with the dischargegap of the lamp and through heating means embodied in the cathodes. Theautomatic switch passes current through the cathodeheating means longenough to bring the oathode(s) of a lamp up to an adequate emissivetemperature, and then suddenly opens the starting circuit, giving riseto a high voltage kick between the electrodes (due to the inductance inthe discharge circuit, and much higher than the operating voltage ofthat circuit) which generally suflices to initiate the discharge.

The time required to preheat the cathodes to the operating temperatureof adequate thermionic emission is appreciable, so that at best anundesirable brief interval elapses between the closing of the wallswitch or other manual switch con-trolling an installation and theactual lighting up of the lamps. Moreover, the action of starters incommon use is often irregular, so that the lapse of time between closingthe control switch and lighting up all the lamps may often amount to aquarter of a minute, more or less. These drawbacks have heretofore beenunavoid- 2 a-ble in practice, because starting of lamps cold, withoutcathode preheat, resulted in rapid disintegration of the cathodes andblackening of the lamps.

Recently, cathodes have been evolved which stand cold starting so muchbetter that it would seem feasible to do away with'hot starting and withstarting switches, so that fluorescent lamps would light instantly (orpractically so) when the controlling switch is closed, just likeincandescent lamps. For this purpose, a leakage-reactance transformermay be used between the lighting supply circuit and the dischargecircuits, to give high open-circuit voltage for initiating discharge,followed by suitably lower voltage for ordinary operation.

While this arrangement is generally successful, it has the disadvantageof requiring larger and more expensive transformers than those now inuse for hot-starting installations, in order to assure starting withcertainty under unfavorable atmospheric conditions of very highhumidity. For example, 40-watt fluorescent lamps of tubular,low-pressure, positive column type may require as high as 800 volts ormore to insure starting under the most adverse conditions, as against avoltage of some 110 volts (more or less) in subsequent operation. Thesize and cost of the auxiliaries for such voltages would be well-nighprohibitive.

I have devised starting arrangements which afford ample voltage toassure starting under the most adverse conditions, without necessity forlarge or expensive auxiliaries, and without the irregularity of startingthat is almost characteristic of certain much-used types of startingswitches. This I accomplish by induced high voltage generated andapplied in a novel way, which is applicable to discharge lamps operatingon D. C., as well as to A. C. systems. For generating and applying thehigh voltage, I employ a capacitor or condenser, an electric valve (e.g., a thyratron, spark-gap, or other auxiliary discharge device) and aninductive coupling to a circuit connected to the main dischargeelectrodes. My invention allows of preheating the cathodes, if desired,without entailing long or irregular delays in starting, as well as ofvirtually instantaneous cold starting without preheat. Various otherfeatures and advantages of the invention will appear from thedescription of a species or form of embodiment, and from the drawings.

In the drawings,

Fig. 1 is a circuit diagram showing starting and operating arrangementsfor discharge 1amp(s operating on A. C); and Fig. 2 is a tilted view ofone form of spark-gap device that is suitable and convenient for use inthe starting circuits illustrated in Fig. 1.

Figs. 3 and 4 illustrate modifications of the Fig. 1 type of circuit toprovide for cathode preheat.

Figs. 1 and 2 illustrate the application of the invention to a dischargedevice I such as the low pressure positive column fluorescent lampeXcrnplified in U. S. Patents No. 2,294,203 to Peters, 2,330,161 toTownsend, and 2,306,925 to Aicher, heretofore ordinarily started hotafter a period of cathode preheat. As shown in Fig. 1, the tubularradiation-transmitting envelope of the device I has spaced-apartactivated thermionic cathodes 2, 2 in its ends. These electrodes 2, 2may be of the usual coiled or coiled-coil tungsten filament type, coatedor charged with activating oxides such as a mixture including barium andstrontium oxides. The envelope may contain a lowpressure atmosphere ofionizable starting gas, such as argon at a pressure of 2 to 4 mm. ofmer-- cury, or other inert rare gas(es) at a corresponding pressure, andalso a vaporizable and ionizable working substance or metal such asmercury, of which a surplus supply (exceeding what will vaporize duringoperation of the device) is indicated by a mercury droplet 3 inside theenvelope. An internal coating of fluorescent material or phosphor 4 onthe envelope walls is also indicated.

The discharge device is shown connected across a discharge circuit 5including the inductive ballast .5. For energizing it, the dischargecircuit 5 is shown connected across the secondary of an autotransformerI whose primary is connected across a voltage source such as an ordinarcycle A. C. lighting circuit 8 of some 110 to 120 volts, for example.The usual make-and-break wall or other control switch 9 is shown in thecircuit 8. To illustrate usual conditions of operation, two similardischarge devices I, I are shown connected across the transformersecondary in parallel lead and lag circuits 5, 5. As usual, the leadcircuit 5 includes a condenser III, which besides other functions alsoserves as ballast to limit the discharge current. Condensers II and I2are shown connected across the lag and lead circuits 5, 5 to preventradio interference, as well under-- stood in the art. I find that thelag circuit condenser II also facilitates starting, though it isnot-essential for this purpose. The transformer I is of course chosen togive or assure the desired voltage across each of the discharge circuits5, 5. Once the discharge has started, the voltage across each device Iis regulated or reduced by its ballast 6 to a favorable value for theoperation of the device I, which may be the closed circuit voltage onwhich the device would be operated in presenthot-starting practice.

For the purposes of my invention, 'a starting circuit I3 is shownconnected across the discharge circuit 5 of each of the dischargedevices I, I. Each circuit I3 is provided with means for generating highvoltage oscillations and applying them across the discharge gap betweenthe electrodes 2, 2 of the corresponding device I, such means comprisinga capacitor or condenser I4 and an auxiliary electric discharge deviceI5 in shunt with one another in said circuit I3, with an inductivecoupling between one side of the shunt and one side of the dischargecircuit 5 to the device I, and, as shown, an impedance I6 in series withthe shunt-connected condenser and auxiliary discharge device orspark-gap. In other words, the circuit l3 here shown includes a loopcircuit I! in which the condenser I4 and sparkgap I5 are connected inparallel, so as to be in series with the rest of circuit I3 includingimpedance I6; and this loop I! also includes a primary IS in inductiverelation to a secondary I9 in the circuit 5, in series with thedischarge device I. Specifically, the inductive primary I8 is shownconnected to the circuit I3 between the sparkgap I5 and the connectionof said circuit I3 to the discharge circuit 5; and the secondary I9 isinterposed in said circuit 5 between said connection of circuit I3 tocircuit 5 and the discharge device I, in series with the latter. Itmakes no difference whether the impedance I6 is connected in saidcircuit I3 at one side of the parallel-connected condenser I4 andspark-gap I5 or at the other side thereof. Nor is it very importantwhich of the direct connections between condenser I4 and spark-gap I5includes the primary I8, or which end of this primary is connected tothe condenser, and which to the spark gap.

The discharge device(s) or spark-gap(s) I5 should have a break-downvoltage less than the open-circuit voltage across the secondary oftransformer 'I, and, therefore, less than the breakdown voltage of anydevice I which the transformer cannot start unaided. The device I5should preferably show a large difference between break-down andmaintaining voltages; :but the maintaining voltage should preferably behigher than the voltage on said device I5 during ordinary operation ofthe discharge devices(s) I, so as to assure cessation of the dischargein device I5 during the ordinary operation of said discharge device(s)I, as hereinafter explained. One suitable device I5 is of moderatelylow-pressure gaseous discharge type, resembling a glow-lamp in generalconstruction, but showing opposite characteristics: i. e., an unstableglow-discharge which is sustained largely by field emission and tends tohot-spot. Such. adevice I4 is illustrated in Fig. 2 as comprising asealed vitreous envelope 2!) containing a flare and stem press type ofmount 2!. with a pair of flat electrodes 22, 22 (resembling halves of acircular disc) suitably spaced apart, and carried by inward-extendingleadwires 23, 23 sealed through the press. These electrodes 22, 22 mayhave a thickness of about inch and a semicircle diameter of about inch.They may consist, for example, of an emissive nickel-tungstencomposition activated with barium, which may be mainly in the form ofbarium oxide, BaO. They may be prepared from a batch mixture of finelydivided ingredients comprising by weight:

Parts W (325 mesh grains) MO 10 BaCOs 10 This mixture is pressed intothe desired shapes in a pill machine, and these are fired for 20 to 30minutes at 1453 to 1510 C. in hydrogen to render them coherent. Inaccordance with U. S, Patent 2,332,809 to Peters, the inner end of thestem press BI is painted with aluminum paint 24 in contact with bothleads 23, 23, to obviate dark effect alterations of break-down voltageof the device.

A mode of operation of the system shown in Fig. l is that when theswitch 9 is closed to turn on the lamps I, I, A. C. voltage is appliedin each discharge circuit 5 and in each starting circuit I3, chargingthe corresponding condenser I4 through the corresponding resistance I6,and also tending to break down the corresponding discharge device' orspark-gap I5. When thedevice I breaks down or becomes conducting, thecondenser I4 discharges through it, producing in the oscillatin-g loopcircuit I! and in the'primary' I8 a current surge or surges, or a seriesof high frequency electrical oscillations. Such break-fdown may occuronce or several times during each 60 cycle or other A. C. wave in thecircuits 8, 5. The rapidly changing current in primary I8 induces insecondary I 9 a high voltage which appears across the discharge gap inthe, discharge device or lamp I and since there is no return path orshunt for this high voltage in I9 except the path through the device I,its full effect is felt in the device I. When such a voltage impulsecoincides with a corresponding impulse due to the A. C. supply incircuit 8, or occurs in such phase relation thereto that the algebraicsum of the voltages sufiices to break down or render conductive thedischarge atmosphere in the device I-which happens in a fraction of asecond after switch 9 is closed discharge in the device I issuccessfully initiated. Moreover, the high frequency from I9 after aglow discharge has started in the device I helps to change this overinto a positive column or are discharge. 1

When the discharge starts, the resistance of the device I falls off to aminor fraction of its value before breakdown (which is of the order ofmegohms), and the voltage across the spark-gap I5 (as limited by theimpedances I, 6, I6, I4, I8 when current is flowing through them)decreases so much that the device I5 drops out and ceases to carrycurrent. During ordinary operation, therefore, current flow in thecircuit I3 is limited by the impedances I6, I4, I8 to a trifling valuewhich may be no more than a couple of milliamperes, representing anenergy loss that is inappreciable.

Because of the high frequency of the electrical oscillations produced asabove. described in the primary I9, the number of turns that are neededin the secondary I9 to produce the desired starting voltage is far lessthan it would be for ordinary commercial frequencies of 60, 50, or 25cycles, so that this secondary and the inductive device or transformerembodying it may be relatively small in size and weight. Foroscillations of sufiiciently high frequency, the transformer I 8, I9 maybe of air-core type, offering only negligible impedance to the currentdue to the 60 cycle or other A. C. in circuit 8. In this case,.theprimary and secondary circuits may or may not be tuned or adjusted tothe same resonant frequency. If the transformer I0, I9 has an iron core,its corresponding impedancemay or may not be negligioperating ballastfor the discharge device I.

However, an iron coremakesfor smaller dimen sions, with less .copper,and; lower secondary resistance.

For the convenience of persons wishing to practi-ce my invention, I willnow give specific details of'design for a system such as shown in Fig.l; but these are to be understood as illustrative, and not as limitingor defining the invention. For starting and operating 40-wattfluorescent lamps of the present T-12, 48 inch tubular, positivecolumn,-low-pressure type, the open-circuit voltageproduced by thetransformer 8 across the discharge circuit(s) 5 may be 300 volts, whichmay obviate the underwriters requirement of special lampholders andwiring with present standard auxiliaries thatgive an open-circuitvoltage of some 450 volts. The condenser I0 may be of 2.1 microfaradcapacity, andthe condensers I I and ble; and in the latter case itbecomespart of the.

I2 of 0.03 microfarad may be of 0.05 mlcrofarad each, and theresistances I6 of 20,000 ohms each. The transformer(s) I8, I9 may be ofauto type, or may have separate primary and secondary windings. Ingeneral, their design is not at all critical. One satisfactoryautotransformer consists of 218 turns of #26 enameled copper wire havinga 1 /2 inch square air core and provided with a primary tap at the fifthturn. In the case of an iron core,

used in this core is that known commercially as DXB, though any goodtransformer iron of the character above indicated is suitable. Tominimize capacitance effects in such a transformefls). I8, I9, the endof the secondary Winding(s) I9 next the core should be connected to thedevice I, and the other end to the ballast 6 through the condenser I0.

For use with a LO-watt fluorescent lamp starting system embodying theparticulars above set forth, the gap between the electrodes 22, 22 maybe about 15 to 20 mils, and the gas filling in the envelope 29 may beargon at a pressure of about to 200 mm. Thus constructed, the device I4.

shows a break-down voltage of about 250 volts R. M. S., and the voltageacross it becomes negative during part of each cycle of the discharge,

voltage in the circuits 8, 5.

Fig 3 illustrates a modification of thesystem shown in Fig. 1 to providefor preheat of the oathodes 2, 2 at starting. In this figure, onl asingle discharge circuit 5 is shown, and the condenser I0 whichdifferentiates lead and lag circuits is omitted, as well as thecondensers II, I2. For preheating purposes, the connection of;each sideof the discharge circuit 5 to one end of a cathode 2 is supplementedwith an auxiliary circuit connection 25 from the other end of saidcathode 2 back to the same sideof the circuit 5, between said cathodeand the secondary I9. In each circuit 25 is included a secondary 26 ininductive relation to a primary that is traversed by current flowing inthe circuit 5, this primary being as shown a current-limiting impedanceI 6 of inductance type in the startin circuit I3. For each electrode 2,therefore, there is a heating part of circuit 25, secondary 26, the restof circuit 25, and the-part of circuit 5 extending fromcircuit 25 backto said electrode 2, and which is energized from circuits 5 and I3. Inpractice the coils I6 and 26, 26 may conveniently be embodied in asingle transformer with double secondaries. In any case, there should beonly a low capacitance between the secondary 26 that is connected to theside of circuit 5 which includes the secondary I9 and the inductivelyassociated parts constituting the rest of the transformer I 6, 26, 26.If for any reason it is not desired to give the primary I6 as muchimpedance as is wanted in the circuit I3, additional impedance I6 may beincluded in said circuit I3.

' In the operation of this system, each cathode 2 is preheated by thecurrent flow in its heating 3 loop from the moment when switch 9 isclosed each. The condensers ll 7 until the discharge is successfullystarted in the device I. While this may often be too short a time tobring this cathode 2 up to full operating temperature and emission,experience has shown that even a relatively small amount of preheatgreatl reduced deterioration of a cathode in.

starting. When the discharge in the device I has been started and thedevice I has dropped out, the current flow in the circuit l3 and in theheating loops of the cathodes 2, 2 is reduced to an insignificant value,so that during ordinary operation the energy consumption in these loopsis trifling.

Besides and because of giving cathode preheat, this system allows ofemploying the same'transformers 8 and ballasts B that are now in use inpresent preheating systems, which give an open circuit voltage of theorder of 200 to 220 volts across the secondary of a transformer 1,instead oi?- requiring a special transformer l' with a secondary voltageof some 300 volts on open circuit, as is' the case with the Fig. 1system.

The modification illustrated in Fig. 4 differs from Fig. 3 in that thesecondaries 2B, 2B in the preheating loops for the cathodes 2, 2 areinductively associated with the primary l8 of the inductive coupling l8,59, instead of with the current-limiting impedance I6. Practically, theprimary l8 and the secondaries I9, 26, 25 may all be embodied in asingle triple-secondary transformer. In this case, the current-limitingimpedance I6 may preferably have a lower value than is preferred in Fig.1, such as some 10,000 ohms, for example.

In Figs. 3 and 4, various parts and features are marked with the samereference characters as those corresponding in earlier figures, in orderto dispense with repetitive description.

In D. C. systems involving my invention, the means for providing thedesired voltage across the discharge circuit will of course he difierentfrom the transformer I here illustrated; the lead and lag circuitfeatures will of course be omitted; and the discharge-controllingballast 6 may be purely resistive instead of inductive or capacitative,or both. However, the starting circuit l3 and the condenser l4,discharge device or sparkgap l5, transformer l8, l9, andcurrent-limiting impedance I6 may be essentially the same as shown inFig. 1.

Figs. 1, 3, and 4 of course assume equipment of each discharge circuit 5with any suitable means (such as sockets diagrammatically represented at21 in dot and dash lines) for electrically connecting it to theelectrodes 2, 2 of each discharge device I, which may be equipped withcorresponding bases or other means, not shown.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The combination with an electric discharge device containing anionizable atmosphere and coacting electrodes, and a discharge circuitconnected to said electrodes, of a starting circuit energized from saiddischarge circuit independently of discharge between said electrodes,including a loop circuit responsive to the voltage supplied to saiddischarge device and a currentlimiting impedance in series with saidloop, a capacitor and an auxiliary electric discharge de vice connectedin said loop in parallel with one another with respect to saidimpedance, said auxiliar discharge device having a break-down voltageless than the supply voltage in said discharge circuit and having amaintaining voltage higher than the voltage thereon during operation 8.of the first-mentioned discharge device, and an inductive couplingbetween said loop and a portion of said discharge circuit which is inseries with the first-mentioned discharge device.

2. The combination with an electric discharge device containing anionizable atmosphere and coacting electrodes, and a discharge circuitconnected to said electrodes, of a starting circuit responsive to thevoltage supplied to said discharge device and connected across saiddischarge circuit in parallel with'the discharge gap between saidelectrodes, including a capacitor'and a sparkgap in shunt wtih oneanother, said spark gap having a break-down voltage less than the supplyvoltage in said discharge circuit and having a maintaining voltagehigher than the voltage thereon during operation of said dischargedevice, and a current-limiting impedance in series with saidshunt-connected condenser and spark-gap,

and a transformer comprising a primary winding capacitor and anauxiliary electric discharge device connected in said loop in parallelwith one another with respect to said impedance, said auxiliary electricdischarge device having a break-down voltage lower than the supplyvoltage in said discharge circuit and having a main taining voltagehigher than the voltage thereon during operation of the first-mentioneddischarge device, and a transformer comprising a primary windingconnected in said loop and a secondary winding connected in saiddischarge circuit in series with the first-mentioned discharge device,between the latter and the corresponding connection of said startingcircuit to said discharge circuit.

4. The combination with an electric discharge circuit and means forconnecting it to coacting electrodes of an electric discharge devicecontaining an ionizable atmosphere, of a starting circuit responsive tothe voltage supplied to said discharge device and connected across saiddis-' charge circuit in parallel with its aforesaid connecting means,and including a loop circuit and a current-limiting impedance in serieswith the loop, a capacitor and an auxiliary electric discharge deviceconnected in said loop in parallel with one another with respect to saidimpedance, said auxiliary discharge device having a breakdown voltageless than the supply voltage in said discharge circuit and having amaintaining voltage higher than the voltage thereon during op-' erationof the first-mentioned discharge device, and an inductive coupling fromsaid loop to a portion of said discharge circuit which lies between itsaforesaid connecting means and its cor-' responding connection to thestarting circuit.

5. Zhe combination with an electric discharge circuit and means forconnecting it to coacting thermionic electrodes of an electric dischargedevice containing an i-onizable atmosphere, of a starting circuitresponsive to the voltage supplied said discharge device and connectedacross said discharge circuit in parallel with its aforesaid connectingmeans, and including a loop circuit and a current-limiting impedance inseries with the loop, a capacitor and an auxiliary electric dischargedevice connected in said loop in parallel with one another with respectto said impedance, said auxiliary discharge device having a breakdownvoltage less than the supply voltage in said discharge circuit andhaving a maintaining voltage higher than the voltage thereon duringoperation of the first-mentioned discharge device, an inductive couplingfrom said loop to a portion of said discharge circuit which lies betweenits aforesaid connecting means and its corresponding connection to thestarting circuit, means forming a heating loop circuit for a thermionicelectrode aforesaid, and an inductive coupling from said heating loop toone of the other circuits aforementioned.

6. In combination, an electric discharge device employing an ionizablemedium and comprising a pair of thermionic electrodes, a dischargecircuit connected to said electrodes, a starting circuit energized fromsaid discharge circuit independently of discharge between saidelectrodes and including said starting circuit responsive to the voltagesupplied to said discharge device, a loop circuit and a current-limitinimpedance in series with said loop, a capacitor and an auxiliaryelectric discharge device connected in said loop in parallel with oneanother with respect to said impedance, said auxiliary discharge devicehaving a break-down voltage less than the supply voltage in saiddischarge circuit and having a maintaining voltage higher than thevoltage thereon during operation of the first-mentioned dischargedevice, and an electrode heating transformer comprising a primarywinding connected in series relation with said impedance and having apair of secondary windings each connected to a different one of saidelectrodes, and an inductive couplin between said loop and a portion ofsaid discharge circuit which is series with the first-mentioneddischarge device.

7. In combination, an electric discharge device employin an ionizablemedium and including a pair of filamentary electrodes, a dischargecircuit connected to said electrodes, a starting circuit energized fromsaid discharge circuit independently of discharge between saidelectrodes and including a loop circuit and a current-limiting impedancein series with said loop, said starting circuit being responsive to thevoltage supplied to said discharge device, a capacitor and an auxiliaryelectric discharge device connected in said loop in parallel with oneanother with respect to said impedance, said auxiliary discharge devicehaving a break-down voltage less than the supply voltage in saiddischarge circuit and havin a maintaining voltage higher than thevoltage thereon during operation of the first-mentioned dischargedevice, and means for coupling said loop and a portion of said dischargecircuit which is in series with the first-mentioned discharge devicecomprising a transforming means having a primary winding connected incircuit with said auxiliary discharge device and said capacitor andincluding a secondary winding connected to one of said electrodes, saidtransformin means also comprising a pair of electrode heating windingseach connected to a difierent one of said electrodes.

DONALD D. HINMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,555,547 Bethenod Sept. 29, 19251,976,645 Westendorp Oct. 9, 1934 2,008,514 Peterson July 16, 19352,050,135 Tour Aug. 4, 1936 2,302,213 Hall Nov. 17, 1942 2,326,597Abernathy Aug. 10, 1943 2,358,810 Karash Sept. 26, 1944

